The present invention relates to a recording format for a high-capacity rewritable optical disk, more specifically to a method for arranging and preserving addresses of recording area identification information, namely the addresses on the optical disk whose groove portions or land portions are allocated as recording tracks.
An example of the track configuration of the conventional optical disk will be described referring to FIG. 16. A plurality of groove tracks 11 and land tracks 12 are arranged alternately in a radial direction of a disk-like recording medium. Each track is wobbled by a small amount in the radial direction. Further, each track is divided into a plurality of circular arc sectors that are arranged in the radial direction, and in a leading part of each circular arc sector, a header 6 having address information used for identifying a recording area is placed. The headers 6 are arranged in the radial directions, i.e., are placed on radial lines. In this example, a width of each track is approximately 0.6 xcexcm and a groove depth of each groove portion is approximately 60 nm. In this example, a length of the sector is approximately 6 mm, which corresponds to a user capacity of 2048 bytes. Each groove portion and each land portion are wobbled by amplitude of approximately 20 nm in the radial direction. The period of the wobble is set at 1/232 times of the sector length, namely, approximately 25 xcexcm. This ratio 1:232 is chosen to correspond the period of the wobble to integral multiples of the length of the record data (channel bit length) such that a recording clock can easily be generated from the wobbles.
FIG. 16 shows details of a sector address header portion in a leading part of the track, namely, an identification information portion. In FIG. 16, pieces of the identification information are placed at two positions, a first position 631 and a second position 632, that are aligned in the radial direction, on the radial lines. The track connects to an immediately previous/subsequent track when making a round, i.e., the groove portion 11 to the groove portion 11 and the land portion 12 to the land portion 12. In this example, each identification information item corresponds to a recording area of an information track at its right. Further, identification information corresponding to the groove part information track 3 is placed at a first position 631, and the identification information corresponding to the inter-groove part information track 4 is placed at a second position 632. That is, pieces of the identification information are placed in such a way that the position thereof along the information track is different from those of adjacent tracks but agree with those of adjacent-but-one tracks. That is, when viewing on boundary lines between the land track and the groove track, the placement position of the identification information is divided into first and second areas, and the first and second identification information areas are used alternately one track by one track.
By this arrangement, for example, when the light spot 21 is scanned on the groove portion 11, the pits on the one boundary line are always reproduced to avoid the crosstalk among one track and the adjacent tracks. Therefore, it becomes possible that the address information placed on the prepits is reproduced without crosstalk. In this example, the address information of the prepits is recorded with an {fraction (8/16)} modulation code (channel bit length =0.14 xcexcm).
The identification information in the header part is composed of small dimples (pits), which are formed due to the unevenness of a substrate or the like together with the grooves etc. when the disk is fabricated.
A phase change type recording film (GeSbTe) is used as a recording film, and a record mark is shaped as an amorphous region.
The foregoing conventional example is described in detail, for example, in Japanese Patent No. 2856390, etc.
However, in applying the above-mentioned conventional technique to high-density recording where recording/reproduction is performed with a blue light source, it was difficult to form small embossed pits in the header parts. Further, the efficiency of the recording track (format efficiency) is reduced because the header part has no grooves and cannot be used as a recording area. Therefore, the prior art is disadvantageous in realizing large capacity in the optical disk.
Another example of conventional methods for recording the address information by means of the wobbles of the groove portion without performing the recording at the sector address header part is described in the international standard ISO/IEC 16969.
In this example, the wobble groove that was frequency-modulated is used in order to record the address data. One round of the disk is composed of about 3,000 wobbles, and 7.5 periods of the wobbles are used to express one bit of the address data. To express bit xe2x80x9c1,xe2x80x9d 4 periods of the 7.5 periods are specified as the first half and the other 3.5 periods are specified as the second half. In other words, the first half is the wobbles of a high frequency and the second half is the wobbles of a low frequency. The frequency ratio is set at 8 to 7. Conversely, bit xe2x80x9c0xe2x80x9d is expressed by the 3.5-period low-frequency wobbles for the first half, and the 4-period high frequency wobbles for the second half. A set of 48 address bits forms an address codeword. 14 bits of the 48 bits of the address codeword are parities for error detection and the leading 4 bits are synchronization information used for establishing synchronization with this codeword. The breakdown of these four bits includes 30 periods of the wobbles (4xc3x977.5), i.e., 12-period high-frequency wobbles, 3.5-period low-frequency wobbles, 4-period high-frequency wobbles, and 10.5-period low-frequency wobbles. The synchronization information can be identified from other data due to the fact that, in the synchronization information, wobbles of the same frequency longer than that of normal address bits by 4 periods or 3.5 periods whereas in a boundary of the normal address bits, wobbles of the same frequency only at 8-period (high-frequency) or 7-period (low-frequency) at most.
However, in the above-mentioned conventional technique, 1 address bit of the address data is expressed by 7.5-period wobbles and the difference in frequency between the first half part and the second half part is not large such that it is difficult to detect a boundary between the first half part and the second half part with high precision by increments of one unit of the wobble period based upon these wobbles. Further, since the synchronization information does not differ so much from other address bits, it is highly likely to be detected mistakenly. Moreover, the parity in the address codeword is 14 bits at most, which is sufficient only for checking errors but not for correcting errors such that the address information can not be reproduced if 1 bit in the address codeword is mistakenly detected It is necessary to secure sufficient S/N of the medium in order to ensure the reliability of address reproduction. When trying to apply this method to the high-density disk that needs the blue light source for reproduction, it is especially difficult to secure sufficient S/N because of the reduced efficiency of blue light detectors.
The first object of the present invention is to provide a high-performance optical disk such that the synchronization can be established easily for the address signal thereof so as to reproduce the address signal at a high speed.
The second object of the present invention is to provide an optical disk in which the address information that can be detected with high reliability.
The third object of the present invention is to provide a method for giving necessary medium information to the rewritable optical disk without using the embossed pits that are difficult to form.
To achieve the objects of the present invention, the following means were used.
(1) In a proposed optical disk, at least one of a groove group including a plurality of grooves and an inter-groove group including a plurality of lands defined by the grooves in the form of a spiral or concentric circles constitutes an information recording area. The optical disk is shaped in the following way. Either the groove group or the inter-groove group is displaced by a small amount in the radial direction according to a combined waveform formed by merging at least a synchronous component of a constant frequency that is not modulated and a signal component that is modulated according to the address data to be recorded in the information recording area.
The small displacement of the grooves, or the lands is usually called the wobble, and a waveform of this wobble can be easily detected by a signal tracking detector (e.g., a push-pull detector etc.). There are an unmodulated component and a modulated component in a detected wobble signal. By using the unmodulated component, disk rotation velocity control and phase synchronization between the phase locked loop (PPL) clock and the reproduced signal can be conducted, and by using the modulated component, the address information can be easily reproduced.
(2) It is specified that a frequency band of the modulated component does not overlap the constant frequency of the unmodulated component.
For example, a waveform made by superposing of an unmodulated fundamental wave and a second harmonic wave that is phase-modulated by 180 degrees so as to easily separate the unmodulated component and the address information and surely detect both signals based upon their frequency difference with a bandpass filter, etc. As such, the first object of the present invention is achieved.
(3) It is recommended that the unmodulated component and the address information are combined in a time-division multiplexing manner such that a period of the combined waveform is equal to or larger than a period of the wobbles and both components have substantially equal periods in time domain.
For example, the unmodulated component is allocated to a front edge of the wobble and the modulated component is allocated to a rear edge thereof. By this arrangement, the synchronization can is performed stably with a PLL circuit for selectively detecting only the front edge and the address information can be obtained by detecting a position of the rear edge.
As another example, a waveform consisting of three edges as a set may be used, wherein one edge remains unmodulated and the other two edges are phase-modulated. Further, as yet another example, the waveform may be composed such a way that a degree of modulation is varied continuously from a modulated part (100%) to an unmodulated part (0%) such that the modulated part and the unmodulated part are allocated alternately and periodically.
In any cases, since the phase synchronization information can be obtained stably by extracting the unmodulated signal component, regardless of the address information, fast synchronization at the time of accessing becomes possible. As such, the first object of the present invention is achieved.
(4) In a proposed optical disk, at least one of a groove group and an inter-groove group in the form of a spiral or concentric circles is allocated as an information recording area. At least one of the groove group and the inter-groove group is wobbled in the radial direction. Pieces of information in the form of binary data or otherwise are assigned to plural kinds of unit wobble waveforms of a constant length. Further, a plurality of said unit wobble waveforms are placed to form a wobble sequence. One bit of the address data or the user data is expressed by at least two kinds of wobble sequences with different arrangements.
For examples, waveforms such as those shown in FIG. 1(a) are used as the plurality of wobble waveforms and one bit of the address data is expressed by a wobble sequence formed by arranging a plurality of these waveforms. In this case, it is recommended that each of plural kinds of wobble sequences be made to be as different as possible (that is, they are made to be mutually different in a plurality of unit wobble waveforms). This is because, if there are many differences between the wobble sequences, even when some of unit wobbles cannot be detected due to an error, such as one caused by defect, the whole reproduced wobble sequence is checked to find which wobble sequence is closest to the original such that the wobble sequence thus chosen is assumed to be the reproduced address data. The larger the difference among the wobble sequences, the more the acceptable number of the mistakenly detected wobbles. Further, a longer wobble sequence (a wobble sequence having a larger number of unit wobble waveforms in it) has higher resistance against erroneous detection. That is, the second object of the present invention is achieved.
(5) The wobble sequence is specified to be in an arrangement that exhibits strong autocorrelation, i.e., selfcorrelation, for a shift by one length or more of the unit wobble waveform.
The strong selfcorrelation has the following property. When the wobble sequence is collated with a wobble sequence generated by shifting (shifting cyclically) per one or more unit wobble waveforms, all the unit wobbles naturally show agreements. The number of agreements is reduced even when there is a slightest shift.
As a wobble sequence having the above property, there is a wobble sequence that can be obtained by allocating different unit wobble waveforms to xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d of a maximum period sequence (M-sequence) which length is limited by the total number of available registers.
A wobble sequence exhibiting strong selfcorrelation can make the PLL circuit synchronize with the reproduced signal accurately with a deviation of less than the length of one unit wobble waveform. If the synchronization to the unit wobble waveform is established by PLL, etc., the synchronization for the unit of 1 bit of the wobble data can be executed for the unit of 1 clock of the phase lock loop (PLL). That is, the first object of the present invention is achieved.
If a plurality of wobble sequences are used to express the address bit, the cross-correlation between different wobble sequences (including a shifted sequence) is preferably as low as possible. That is, it is undesirable to choose a wobble sequence that is susceptible to be mistaken as a different wobble sequence to establish erroneous synchronization. Preferably, the wobble sequence is selected such that the degree of the cross-correlation is kept two-thirds or less of the degree of selfcorrelation.
(6) In a proposed optical disk, at least one of a groove group and an inter-groove group in the form of a spiral or concentric circles constitutes an information recording area. At least one of the groove group and the inter-groove group is wobbled in the radial direction. A plurality of wobbles form the address codeword used for identifying the information recording area. Further, a plurality of wobble sequences for synchronization are placed in the said address codeword
(In a proposed optical disk, at least one of a groove group and an inter-groove group in the form of a spiral or concentric circles constitutes an information recording area. At least one of the groove group and the inter-groove group is wobbled in the radial direction. A plurality of wobbles form the address codeword used for identifying the recording area, and the address code is divided and placed in a plurality of synchronization frames that are partitioned by the wobble sequences used for synchronization.
The above means can establish synchronization in a time period shorter than that is required to reproduce the address codeword itself. As such, the second object of the present invention is achieved.
Further, since plural pieces of synchronization information are placed in a single codeword, redundancy is provided for the synchronization information itself such that, the reliability against loss and erroneous detection of the synchronization information is ensured. Moreover, even if synchronization is lost or tracking error occurs, its information can be detected in a shorter time so as to ensure high reliability. Here a desirable arrangement is described.
(8) Preferably, the above-mentioned wobble sequence used for synchronization is composed of plural kinds of arrangements, and preferably such plural kinds of sequences are placed so that their positions in the address codeword can be specified with the difference in order or with the arrangement of the plural kinds of wobble sequences placed in the address codeword.
In other words, it is desirable that the synchronization information is not of one kind but of plural kinds and pieces of the synchronization information are placed in the codeword so as to be different according to its position therein. With this condition, the synchronization of the codeword can be established by reproducing part of plural pieces of synchronization information in the codeword.
(9) In a proposed optical disk, at least one of a groove group and an inter-groove group in the form of a spiral or concentric circles constitutes an information recording area. At least one of the groove group or the inter-groove group is wobbled in the radial direction. A plurality of wobbles form the address codeword used for identifying the recording area. Additional data other than the address information may be placed in the said address codeword. Further, plural pieces of additional data placed in a plurality of address codewords are integrated to form a code block for correcting errors of the additional data.
By this arrangement, necessary medium information etc. can be provided to the rewritable optical disk without using the embossed pits that are difficult to form. As such, the third object of the present invention can be achieved. In this case, since the additional information is added with an error correction code, information can be surely reproduced even via a medium with a defect.
(10) The disk stores, as the above-mentioned additional data, control information for protecting the data or cryptographic key information for restricting accesses when the data is being recorded or reproduced; or
(11) The optical disk stores control information specifying a type of disk and characteristics thereof as the above-mentioned additional data.
These are pieces of information that are hitherto recorded using embossed data in the prior art, but the present invention provides the same benefits without using the embossed data so-as to provide inexpensive disks.